Conventionally, an impact tool such as a hammer drill or a hammer driver is capable of applying an impact force to a tip tool. Such an impact tool has: a casing; a tip tool which is rotated by an electric motor provided in the casing; a striker which is provided so as to be linearly reciprocable in the casing; a motion converting mechanism which converts rotary motion of the electric motor to reciprocating motion of a piston; and a striker which transmits the impact force generated by the reciprocating motion of the piston to the tip tool. In the impact tool, the casing vibrates due to the reciprocating motion of the piston, the movement of striking the tip tool by the striker, and others. For this reason, techniques by which the vibrations of the casing in the impact tool can be reduced have been proposed, and an example thereof is described in Patent Literature 1.
An impact tool described in Patent Literature 1 has a hollow casing, and the interior of the casing is separated into a first housing chamber, a second housing chamber, and a third housing chamber by two partition walls. An electric motor is provided in the first housing chamber. The electric motor has an output shaft, and is configured so that the output shaft is rotated when electric power of an external power supply is supplied.
Bearings are attached to the two partition walls, respectively, and a first intermediate shaft is supported by the bearing to be rotatable about a first center line. The first intermediate shaft is disposed across the second housing chamber and the third housing chamber. The output shaft and the first intermediate shaft are coaxially provided, and the output shaft and the first intermediate shaft are coupled so as to be integrally rotated. A first gear is provided at a part of the first intermediate shaft which is positioned in the third housing chamber.
Also, a second intermediate shaft is provided in the third housing chamber, and the second intermediate shaft is supported by two bearings to be rotatable about a second center line. The second intermediate shaft is provided with a second gear, and the first gear and the second gear mesh with each other. Furthermore, the second intermediate shaft is provided with a gear part. Moreover, the third housing chamber is provided with a cylinder having a cylindrical shape, and in the cylinder, a piston, a striker, an intermediate element, and a tip tool are inserted to be reciprocable in a direction along a third center line (center line) of the cylinder. A pneumatic chamber is formed between the piston and the striker in the cylinder. All of the first center line, the second center line, and the third center line are mutually parallel. The tip tool is provided so as to rotate integrally with the cylinder, and a tip of the tip tool is exposed to the outside of the cylinder. A third gear is attached to the cylinder, and the third gear and the gear part mesh with each other. Furthermore, a sleeve having a cylindrical shape is attached to an outer peripheral surface of the second intermediate shaft so as to be relatively rotatable with the second intermediate shaft. In the third housing chamber, a clutch which engages and releases the sleeve and the second intermediate shaft is provided. Moreover, the clutch is configured so that actuations are switched by the operation of a change lever. Furthermore, a motion converting mechanism which converts rotary motion of the sleeve to reciprocating motion of the piston is provided in the third housing chamber.
On the other hand, a vibration reducing mechanism is provided in the second housing chamber. The vibration reducing mechanism has a supporting member which is fixed to a casing and a counter weight which is attached to the supporting member via a plate spring. A shaft hole is provided in the counter weight, and the second intermediate shaft is inserted in the shaft hole. Also, a handle part is provided at an end part of the casing on an opposite side of an attachment part of the tip tool. The handle part is provided with a trigger. Furthermore, a grip part is attached near the attachment part of the tip tool in the casing.
In the impact tool described in the Patent Literature 1 mentioned above, an operator holds the handle part with one hand, holds the grip part with the other hand, and presses the tip tool to an object. Then, by the operation of the trigger, electric power is supplied to the electric motor, and the output shaft rotates. The torque of the output shaft is transmitted to the cylinder via the first intermediate shaft and the second intermediate shaft. The tip tool is rotated together with the cylinder.
At this point, if a drill mode is selected by the operation of the change lever, the clutch is released, the torque of the second intermediate shaft is not transmitted to the sleeve, and the second intermediate shaft and the sleeve relatively rotate. In this manner, the tip tool rotates, and striking by the striker is not carried out.
On the other hand, if a hammer drill mode is selected by the operation of the change lever, the clutch is engaged. Therefore, the torque of the second intermediate shaft is transmitted to the sleeve, and the second intermediate shaft and the sleeve integrally rotate. The rotary motion of the sleeve is converted to reciprocating motion of the piston by the motion converting mechanism. When the piston reciprocates in the cylinder, the pneumatic pressure in the pneumatic chamber is rapidly increased to generate impact force. This impact force is transmitted to the tip tool via the striker and the intermediate element.
In the impact tool described in Patent Literature 1, vibrations caused by the reciprocating motion of the piston and the striking motion of the striker are generated, and the vibrations are transmitted to the counter weight via the casing, the supporting member, and the plate spring. Then, the counter weight vibrates in the same direction and the counter direction to the reciprocating motion of the piston, and the vibrations of the casing are assumed to be reduced.